Field of the Invention
The present invention relates to a fixing member for use in a fixing device of an image forming apparatus employing an electrophotographic system and a method for manufacturing the same.
Description of the Related Art
In an electrophotographic image forming apparatus, such as a copying machine and a laser beam printer, a system employing a fixing member, such as a fixing roller or a fixing belt, has been adopted as a method for fixing a non-fixed toner image on a recording material by heat or pressure. In this system, a fixing member as a rotation member for heating and a rotation member for pressing (pressing member) which are disposed in such a manner as to form a pair therewith are brought into pressure contact with each other to form a nip portion. Then, due to the fact that a recording material, such as paper, bearing a non-fixed toner image passes through the nip portion, the toner is melted and pressed to form a fixed image.
Used as the fixing member are those having a configuration in which an elastic layer containing a heat-resistant rubber, such as silicone rubber, and a release layer containing a fluororesin are successively formed on the outer surface of a substrate. As a method for producing such a fixing member, a method is mentioned which includes applying a coating solution for forming a release layer (aqueous dispersion coating solution) containing fluororesin particles to the surface of an elastic layer to form a coating film, and then heating the coating film to a temperature equal to or higher than the melting point of the fluororesin for baking (hereinafter referred to as a “coating method”).
However, in the coating method, during the heating of the coating film, the elastic layer containing a silicone rubber is also heated and expands as the temperature of the elastic layer rises. The expansion of the elastic layer may result in a formation of a crack in the release layer.
Japanese Patent Laid-Open No. 2006-205151 discloses a process for preventing a crack formation in a surface layer formed by the coating method. It discloses in paragraph 0028 that as a coating liquid for forming a release layer, it is preferable to use a fluororesin dispersion containing a film forming agent such as a water soluble acrylic resin. The film forming agent is considered to bind a fluororesin particles dispersed in the fluororesin dispersion until the fluororesin particles start melting, and therefore, formation of a crack in the surface layer is considered to be prevented.
On the other hand, the fixing member has been demanded to have higher durability with an increase in the printing speed in recent years. As a fixing member excellent in durability, Japanese Patent Laid-Open No. 2003-167462 describes a fixing member obtained by coating a fluororesin having a melt viscosity (Melt flow rate (MFR)) of 1 g/10 min to 3 g/10 min, and then baking the coating.